FUDGEM=0 in EMFCUT still allowed

Physics, Transport and Magnetic Fields
1

Hi everyone,
I stumbled upon a case where the transport card EMFCUT with the wrong FUDGEM value was running instead of crashing as the FUDGEM=0 should be a “not allowed condition” according to the last manual.

*...+....1....+....2....+....3....+....4....+....5....+....6....+....7....+....
EMFCUT        -1E-06      1E-6         0  HYDROGEN  @LASTMAT          PROD-CUT

This issue is similar to https://fluka-forum.web.cern.ch/t/emf-cut-problems-about-what-3/847
but while Honghu had not default (and therefore an error) I had instead 0 (by mistake) and - as the simulation was running - I didn’t realize that until I had to change the transport and production energies.

My bad clearly. One should always check the physics setting before running.

In order to evaluate how is the effect of this on older simulations which I run - and save kW of CPU power to rerun the simulation - I would like to know (if possible) how is this FUDGEM=0 interpreted by the code.

Thank you in advance for you help!
Best
Vittorio

P.S. (edited) the notes in the manual have also an example where FUDGEM is set to 0

     Example 1 (number-based):

 *...+....1....+....2....+....3....+....4....+....5....+....6....+....7...
 EMFCUT       -1.0E-5    1.0E-5       0.0       4.0       8.0          PROD-CUT
 *   A production threshold of 10 keV is set for electrons, positrons and
 *   photons in all materials from 4 to 8.

     The same example, name-based:

 EMFCUT       -1.0E-5    1.0E-5       0.0    HELIUM    OXYGEN          PROD-CUT
3

Hi Vittorio,
good news: actually FUDGEM=0 is the correct value for your low threshold (< 5 keV), so no crash was due. The manual is actually misleading and should be properly amended, thanks.
This input parameter rules the calculation of the contribution of atomic electrons to electron/positron multiple scattering, as discussed in the former post you quote. For very low electron threshold (< 5 keV), this contribution is already taken into account by explicit secondary electron generation, so it should be zeroed, as you did. (Note that 0 and blank are in fact the same thing). The opposite is true for higher electron thresholds: since low energy secondary electrons are no longer generated, this contribution should be valued and FUDGEM=0 is no longer permitted by the code, hence the legitimate abort previously reported. (Nevertheless, the user is still allowed to intentionally suppress it by putting a minimal value).

1 Like
4

Thanks loads @ceruttif, love to hear that.
Tons of CO2 were saved :slight_smile:

For very low transport and production thresholds (10 keV) I use typically 1e-5, but this is not an usual case (plus things are very CPU intensive at low thresholds).

Thanks again. All the best.

5

I expect you use 1 from ~50 keV onward.